1. Field of the Invention
The present invention relates to a spindle motor for a hard disc drive, and particularly, to a spindle motor for a hard disc drive having an oil outflow prevention apparatus preventing outflow of oil from a fluid dynamic bearing used in the spindle motor.
2. Description of the Related Art
In general, a spindle motor, used in a hard disc drive, having a large capacity and a high rotational speed, utilizes a fluid dynamic bearing having less driving friction than a ball bearing for reducing noise and non-repeatable run-out (NRRO) in the hard disc drive. The fluid dynamic bearing forms an oil film between a rotating member and a fixed member, and is able to support the rotating member with pressure generated during rotation. Accordingly, the rotating member and the fixed member can be kept from direct contact, and frictional resistances can be reduced. In order to effectively generate a required pressure to form the oil film, a groove, used in generating dynamic pressure, is formed, e.g., in a spiral pattern, on the rotating member and at least one side of the fixed member.
Accordingly, a radial bearing having a groove used in generating dynamic pressure is formed on a circumferential surface so that oil in bearing clearances, with respect to a sleeve, can support a load in the radial direction of the shaft with the dynamic pressure generated by the groove. Further, a thrust bearing, having grooves used in generating dynamic pressure, is formed on upper and lower surfaces of a thrust plate so that oil in bearing clearances, with respect to a shaft and a sleeve, can support a load in the axial direction of the shaft. The dynamic pressure generated by the grooves facilitates stable operations.
FIG. 1 is a side, cross-sectional view of a conventional spindle motor having a radial bearing, as well as a thrust bearing, to support loads in the radial and axial directions of a shaft thereof.
Referring to FIG. 1, bearing clearances are provided between a shaft 150 and a sleeve 130 of a spindle motor 100. Grooves 131, used in generating dynamic pressure, are formed at upper and lower sections of the inner circumferential surface of the sleeve 130.
A base 110 is positioned at a lower section of the shaft 150, and a thrust plate 151 and a thrust flange 153 are mounted on the base 110. Although not shown in FIG. 1, grooves (not shown) used in generating dynamic pressure between the thrust plate 151, the thrust flange 153, and the sleeve 130 are also provided.
The bearing clearances are provided to form a path between the sleeve 130, the outer circumferential surface of the shaft 150, the thrust plate 151, and the thrust flange 153.
An oil inlet 160 is provided at one side of the sleeve 130 through the outer circumferential surface to the inner circumferential surface thereof. The oil inlet 160 is also provided at the base 110 adjacent to the side of the flange 153. Oil, provided through the oil inlet 160, is filled into the bearing clearances to support the shaft 150, with the pressure generated by the grooves, when the shaft 150 is rotated.
In the conventional hard disc drive spindle motor, having a structure as described above, as the shaft is rotated, the oil is subject to heat generated by friction. As temperature increases, due to frictional heat generated in the bearing clearances, the air bubbles in the oil, provided into the bearing clearances, are thermally expanded. Consequently, a problem occurs in that non-repeatable run-out (NRRO) critical to driving characteristics, driving resistances, and consumption power increases. Therefore, a separate vent is formed, or the oil inlet as shown in FIG. 1, is used to eliminate the air bubbles from the bearing clearances.
FIG. 2 shows a state in which the oil flows out from the conventional spindle motor shown in FIG. 1. Referring to FIG. 2, as the air bubbles flow out through the oil inlet 160, the oil also flows out from the bearing clearances. The oil, that has flowed out, contaminates the inside of the spindle motor. Further, as the oil has flowed out, a deficiency of oil in the bearing clearances occurs. Accordingly, abrasion of frictional members is accelerated and their life cycles are reduced, or in a severe case, the spindle motor cannot be driven.
In addition, fine metal particles, produced during the assembly of the frictional members, can be mixed with the oil in the bearing clearances. The metal particles can cause damage to the frictional surface of the shaft, or obstruct the driving of the motor as they flow out with the oil.